KR100965892B1 - Optical scanning apparatus and image forming apparatus employing the same - Google Patents

Abstract

Disclosed are a recording / playback apparatus and method for an optical disc. The disclosed recording / reproducing apparatus is a recording / reproducing apparatus for an optical disc having an optical information storage layer, wherein the focus of reference light is formed in the optical information storage layer, and the reference light includes an objective lens facing the optical disc. Optical system; A signal light optical system for forming a focus of a signal light in the optical information storage layer, the signal light optical system including the objective lens; Servo optical system for irradiating the servo light to the optical disk and receiving the reflected light to perform focusing and tracking control of the objective lens, the reference optical system includes a first focusing unit for moving the focus of the reference light; And the signal light optical system includes a second focusing unit for shifting the focus of the signal light, wherein the first focus position of the reference light and the focus of the signal light coincide with each other in the optical information storage layer. By moving and forming information in the thickness direction, the information is recorded in the plurality of recording layers.

Description

Apparatus and method for recording / reproducing an optical disc {Optical scanning apparatus and image forming apparatus employing the same}

The disclosed optical disc recording / reproducing apparatus and method relate to an optical recording / reproducing technique, and more particularly, to a recording / reproducing technique for an optical disc in which information can be recorded in a plurality of recording layers.

The information storage capacity of an optical information storage medium (hereinafter referred to as an optical disc) is rapidly increasing with the development of related technologies. Optical discs may include compact discs (CDs), digital versatile discs (DVDs), HD-DVDs, and Blu-ray discs according to information storage capacities.

In addition, recently, information storage technology using holograms has attracted attention. The hologram optical disk uses a photosensitive material such as inorganic crystal or photopolymer which is sensitive to light as a material of the recording layer, and the information is transmitted in the form of two interfering laser beams, namely, an interference fringe by reference light and signal light. Stored in the photosensitive material. Further, when reference light similar to the reference light at the time of recording is irradiated to the hologram optical disc in which the information is stored in the form of an interference fringe, the information is reproduced while the signal light is restored.

Such hologram information storage technology uses a volume holography method for recording / reproducing pages by volume using volume holography and a micro-recording / reproducing method for single bits using micro holography. There is a holography method. Volume holography has the advantage of processing a large amount of information at the same time, but because the optical system has to be adjusted very precisely there is a problem that it is difficult to be commercialized as an information storage device for the general consumer.

On the other hand, the micro-holography method forms a fine interference pattern (micro hologram) by interfering two focused light at the focal point, and moving the interference pattern on the plane of the information storage medium to record a large number to form a recording layer. The recording layer is formed in a multi-layer by overlapping in the depth direction of the information storage medium to record information in three dimensions on the holographic information storage medium.

Basically, the micro-holography method increases the capacity by recording the multilayered material in the depth direction of the holographic information storage medium. In a multi-layer optical disc such as a BD (Blu-ray Disc), there is a reflective film that physically distinguishes each recording layer, so that a plurality of recording layers are distinguished by using the level of the reflected light intensity signal and the polarity of the signal, Make focus.

However, in the case of a hologram optical disc, unlike a conventional optical disc, there is no reflective film for physically distinguishing a plurality of recording layers. Therefore, it is difficult to form an optical focus at a desired recording layer position of the holographic optical disk, and a study on a method of recording / reproducing a plurality of recording layers of the holographic optical disk is required.

In accordance with the above-mentioned necessity, embodiments of the present invention provide an apparatus and method for performing recording / reproducing for an optical disc on which information can be recorded in a plurality of recording layers.

A recording / reproducing apparatus according to an embodiment of the present invention is a recording / reproducing apparatus for an optical disc having an optical information storage layer, wherein the focus of a reference light is formed in the optical information storage layer and faces the optical disk. A reference light optical system including an objective lens; A signal light optical system for forming a focus of a signal light in the optical information storage layer, the signal light optical system including the objective lens; Servo optical system for irradiating the servo light to the optical disk and receiving the reflected light to perform focusing and tracking control of the objective lens, the reference optical system includes a first focusing unit for moving the focus of the reference light; And the signal light optical system includes a second focusing unit for shifting the focus of the signal light, wherein the first focus position of the reference light and the focus of the signal light coincide with each other in the optical information storage layer. By moving and forming information in the thickness direction, the information is recorded in the plurality of recording layers.

The optical disk does not have a reflective film for physically distinguishing the plurality of recording layers, and the optical information storage layer of the optical disk may be made of a photosensitive material capable of hologram recording.

When the first focusing position is moved to a second focusing position having a different thickness direction position of the optical information storage layer, the first and second focuses of the first light and the second light are simultaneously moved to the second focusing position. The focus shift unit may be driven.

When the first focusing position is moved, the first and second focusing units may be driven such that a focus error signal due to a mismatch between the focus of the first light and the focus of the second light is within the negative feedback linear section.

When moving the first focus position, the servo operation of the servo optical system can be maintained.

In a recording / reproducing method for an optical disc according to an embodiment of the present invention, in the recording / reproducing method for an optical disc having an optical information storage layer, the focus of the first light and the focus of the second light are formed on the optical information storage layer. Making; Moving the focal point of the first light and the focal point of the second light to coincide at the first focal position, and changing the first focal point along the thickness direction of the optical information storage layer in the optical information storage layer and recording information; Information is recorded in a plurality of recording layers, including;

When the first focus position is changed to a second focus position having a different thickness direction position of the optical information storage layer, the focus of the first light and the focus of the second light may be simultaneously moved to the second focus position. .

When the first focus position is shifted, the focus error signal due to a mismatch between the focus of the first light and the focus of the second light may shift the focus of the first light and the focus of the second light so as to be within a negative feedback linear section.

When the first focusing position is moved, the servo driving operation of the objective lens forming the focal point of the first light and the focal point of the second light can be maintained.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, like reference numerals refer to like elements, and the size of each element in the drawings may be exaggerated for clarity and convenience of description.

1 is a view showing a schematic structure of a hologram optical disk that can be applied to a recording / reproducing apparatus according to an embodiment of the present invention, and FIG. 2 is formed in the optical information storage layer of the optical disk of FIG. Fig. 1 shows a schematic recording mark hologram.

Referring to FIG. 1, the optical disc 10 includes a substrate 14, 15, a reflective film 11 reflecting light of a first wavelength, and a light of a first wavelength, which is different from the first light. The light having a second wavelength includes a reflective transmission film 12 which reflects light, and an optical information storage layer 13 on which optical information is recorded. The light of the first wavelength may be red light, which is servo light, and the light of the second wavelength may be blue light. In the optical information storage layer 13, information may be recorded in a plurality of recording layers, but a reflective film for physically distinguishing the plurality of recording layers is not formed. For example, the optical information storage layer 13 may be a photosensitive material capable of hologram recording. In the figure, Lr1 and Lr2 represent servo light incident on the reflective film 11 and servo light reflected on the reflective film 11, respectively. Lb1 and Lb3 represent the reference light focused at the focus Fb and the reference light emitted after being focused at the focus Fb and reflected by the reflective transmission film 12, respectively. Lb2 and Lb4 represent signal light that is reflected by the reflective transmission film 12 and then focuses on the focus Fb, and the reflected signal light that passes through the focus Fb. Fb represents the focus of the reference light.

The optical disc 10, like the conventional CD, DVD, BD, is, for example, a disk shape of 120 mm in diameter with a hole formed in the center thereof, and the holographic information storage medium to protect the optical information storage layer 13 and the reflective film 11. (10) Substrates 14 and 15 may be formed on both sides. The substrates 14 and 15 may be made of a material such as polycarbonate or glass.

The optical information storage layer 13 may be made of a photo polymer having a refractive index that changes depending on the light intensity irradiated. For example, the optical information storage layer 13 may be provided to react to blue light having a wavelength of about 405 nm. When the reference light Lb1 which is blue light and the signal light Lb2 interfere with the optical information storage layer 13, a hologram which is a recording mark is formed as shown in FIG. The recording mark hologram formed at this time may be a micro hologram. The substrates 14 and 15 may be formed to have the same refractive index as that of the optical information storage layer 13.

 The thickness d2 of the optical information storage layer 13 is designed to be sufficiently larger than the height of the recording mark. For example, the optical information storage layer 13 may be designed to a thickness of about 150 μm. In FIG. 1, d1 represents the thickness of the substrate 14 from the surface to the optical information storage layer 13, d2 represents the thickness of the optical information storage layer 13, and d3 represents the reflective transmission film 12 to the reflective film 11. Indicates the thickness.

In the optical information storage layer 13, one recording layer is formed in accordance with the hologram recording caused by the interference of the signal light Lb2 and the reference light Lb1, and the recording is performed while changing the position where the hologram recording is made in the depth direction. Information can be recorded in layers.

Land, grooves, or pits may be formed in the reflective film 11 to implement tracking and focusing servos. Servo light Lr1 which is light of a first wavelength incident from the substrate 14 side, for example, red light, is reflected by the reflective film 11 toward the substrate 14 side.

The reflective transparent film 12 is a wavelength selective reflective film that transmits servo light (red light) and reflects light of a second wavelength, for example, blue light. The reflective transparent film 12 may be formed of a cholesteric liquid crystal layer to have a circularly polarized light separation function. A cholesteric liquid crystal layer having a circular polarization separation function has a selective reflection characteristic that reflects only the circular polarization component when the rotation direction (right or left rotation) of the liquid crystal spiral coincides with the circular polarization direction and the wavelength is the spiral pitch of the liquid crystal. Have For example, when blue light is incident from the substrate 14 side with right circularly polarized light, the light reflected by the reflective transmission film 12 becomes right circularly polarized light.

The signal light Lb2 is reflected by the reflective transmission film 12 and then focused on the focus Fb, and the reference light Lb1 is immediately focused on the focus FLb. In this case, the signal light Lb2 may be incident on the optical disk 10, for example, right circularly polarized light, and the reference light Lb1 may be incident, for example, by left circularly polarized light. In consideration of this, the reflective transmission film 12 may be provided to basically reflect, for example, the signal light Lb2 which is blue light of right circularly polarized light and transmit the reference light Lb1 which is blue light of orthogonal left circularly polarized light.

3 is a diagram schematically illustrating a process of recording information in a plurality of recording layers on an optical disc in the recording / reproducing method according to the embodiment of the present invention.

The drawing shows that the signal light Lb2 and the reference light Lb1 form a focal point for information recording in the optical information storage layer 13 where information is recorded on the optical disc 10 of FIG. 1, and the reflective layer RL is a reflective film. FIG. 1 schematically shows a configuration including (11 in FIG. 1) and a reflective transparent film (12 in FIG. 1). The focus direction indicates the thickness direction of the optical information storage layer 13, and the radial direction indicates the direction traversing the track in the radial direction of the optical disc, that is, the tracking direction, and is tangential. The direction represents the circumferential direction in the direction along the track of the optical disc.

As described above in the description of FIG. 1, information is recorded in the optical information storage layer 13 in the form of interference fringes of the reference light Lb1 and the signal light Lb2, and at this time, the position at which the information is recorded is the reference light. The focus of Lb1 and the signal light Lb2 is determined to coincide at the first focal point position Fb.The reference light Lb1 and the signal light Lb2 are determined by a predetermined optical system including the objective lens 100. The focal point of the optical information storage layer 13 may be formed, and the focus of the reference light Lb1 and the focus of the signal light Lb2 may be moved along the thickness direction of the optical information storage layer 13, that is, the focus direction. In addition, the servo light Lr1 is irradiated for servo control of the objective lens 100 with respect to the optical disk, Fig. 4 shows a detailed configuration of the optical system for forming the reference light Lb1, the signal light Lb2, and the servo light Lr1. Will be described later in the description with respect to FIG.

In order to record information in the optical information storage layer 13 in a plurality of recording layers, the first focus position Fb where the focus of the reference light Lb1 and the focus of the signal light Lb2 coincide with each other must be changed in the focus direction. To this end, the focus of the reference light Lb1 is shifted in the focus direction, and the focus of the signal light Lb2 is shifted in the focus direction. In the drawing, it is shown that the first focus position Fb is moved from the second focus position Fb '. In the embodiment of the present invention, when the first focus position Fb is changed to the second focus position Fb ', the focus of the reference light Lb1 and the focus of the signal light Lb2 are simultaneously moved to the second focus position Fb'. The method of moving is adopted. This method is selected so that the recording layer can be changed stably and quickly when recording information. For example, in a method in which the focus of the signal light Lb2 is sequentially moved to the second focus position Fb 'and then the focus of the reference light Lb1 is moved to the second focus position Fb'. After moving the focus to the second focus position Fb ', the servo drive to the optical disk of the objective lens 100 should be turned off, and the servo after moving the focus of the signal light Lb2 to the second focus position Fb'. The driving should be started, which may lower the operational stability when changing the recording layer.

As in the embodiment of the present invention, when the focal point of the reference light Lb1 and the focal point of the signal light Lb2 are simultaneously moved to the second focal point position Fb ', the servo drive can be continuously maintained during the movement. Here, the term "simultaneously" means that the time when the focus of the reference light Lb1 and the focus of the signal light Lb2 are at the first focal position Fb and the second focal position Fb 'are completely coincident with each other. This does not mean that the operation of shifting the focus of the reference light Lb1 and the operation of shifting the focus of the signal light Lb2 do not occur sequentially but rather occur together. When moving from the first focus position Fb to the second focus position Fb ', the degree of mismatch between the focus of the reference light Lb1 and the focus of the signal light Lb2 is indicated by the focus error signal FES. It is necessary to keep the FES signal into the linear negative feedback region in order for the movement to be made without this, which can be confirmed by the RFDC indicating the confocal signal level.

In the case of changing the recording layer according to the above-described method, recording / reproducing stably for an optical disc that does not have a reflective film for physically distinguishing a plurality of recording layers, for example, a hologram optical disc for recording information in a hologram manner can do.

4 is a view schematically showing the configuration of a recording / reproducing apparatus according to an embodiment of the present invention. For example, the recording / reproducing method described in FIG. 3 may be performed by such a recording / reproducing apparatus.

Referring to FIG. 4, the recording / reproducing apparatus according to the embodiment of the present invention forms a path of servo light for servo driving the objective lens 100 that condenses the light for recording / reproducing information on the optical disc 10. A signal light optical system 50 for forming a focus of the servo optical system 70 and the signal light Lb2 in the optical information storage layer of the optical disc 10; And a reference light optical system 20 for forming a focus of the reference light Lb1 in the optical information storage layer. The signal light optical system 50 and the reference light optical system 20 form a recording / reproducing optical system. In the embodiment of the present invention, the signal light optical system 50 and the reference light optical system 20 respectively move the focus of the signal light Lb2 and the focus light of the reference light Lb1 in the optical information storage layer of the optical disc 10. It is provided.

Hereinafter, more detailed configurations of the servo optical system 70, the signal optical optical system 50, and the reference optical optical system 20 will be described with reference to FIGS. 5, 6, and 7.

FIG. 5 is a view schematically showing an embodiment of a traveling path of servo light in the servo optical system 70 in the recording / reproducing apparatus of FIG. 3.

Referring to FIG. 5, the servo optical system 70 irradiates the optical disk 10 with the first light having the first wavelength emitted from the first light source 71, that is, the servo light Lr1 having a red wavelength, and reflecting film 11. It may be configured to receive the servo light (Lr2) reflected from.

For example, the first light source 71 may emit servo light Lr1 having a wavelength of about 660 nm. The servo light Lr1 emitted from the first light source 71 is divided into three such as one main beam and two subbeams by the grating 72, and passes through the polarization beam splitter 73 to collimate the lens 74. Is incident on.

The grating 72 may be configured to diverge the amount of light of the main beam to a greater or equal level than the subbeam. In FIG. 5, the subbeams are omitted. The polarization beam splitter 73 may be configured to transmit the P-polarized component and reflect the S-polarized component of the incident servo light Lr1. The collimating lens 74 converts the servo light Lr1 emitted from the light source 71 into parallel light. The servo light Lr1 converted into parallel light is incident on the correction lens 75. The correction lens 75 may be composed of two focusing lenses 76 and 77. The servo light Lr1 passing through the correction lens 75 passes through the dichroic prisms 40 and 41, is reflected by the mirror 42, is incident on the quarter-wave plate QWP 43, and is converted into circularly polarized light. Is incident on the lens 100. As shown in FIG. 1, the objective lens 100 focuses the servo light Lr1 on the reflective film 11 to form a focal point Fr on the reflective film 11, and is reflected by the reflective film 11 to enter the servo light Lr1. ) And the reflected servo light Lr2 proceeds in the opposite direction.

The objective lens 100 is designed to be optimized for the second light of the second wavelength emitted from the second light source 21, that is, the blue light for hologram recording / reproducing, and the first light of the first wavelength, that is, the servo light Lr1. For the servo light Lr1, the servo light Lr1 is optimized to be focused on the reflective film 11 by the relation of the optical distance between the correction lens 75 and the objective lens 100. It can act as a condenser lens of 0.63.

The dichroic prism 40 transmits almost 100% of red light (servo light) and reflects almost 100% of blue light (reference light in the optical system of FIG. 7 as hologram recording / reproducing light), and the dichroic prism 41 has almost 100% red light. For example, the p-polarized component of the blue light may transmit nearly 100%, and for example, the s-polarized component may be arranged to reflect nearly 100%. The mirror 42 reflects almost 100% of both the red light and the blue light, and the quarter wave plate 43 can convert the linearly polarized light into the circularly polarized light in both the red light and the blue light.

The reflected servo light Lr2 sequentially passes through the objective lens 100, the quarter-wave plate 43, the mirror 42, the dichroic prism 40, 41, and the correction lens 75 and becomes a parallel beam. The light is collected by the collimating lens 74, reflected by the polarization beam splitter 73, and received by the first photodetector 79. An astigmatism lens, for example, a cylindrical lens, is formed between the polarizing beam splitter 73 and the first photodetector 79 so as to generate astigmatism in the reflected servo light Lr2 to implement focus servo by the astigmatism method. : 78) may be further provided.

Since the optical disc 10 has a possibility of deflection and eccentricity, there is a possibility that the target track and the corresponding focal position change. Therefore, in the servo optical system 70, it is necessary to position the focus of the servo light Lr1 at the target track and the corresponding focus. For this purpose, it is necessary to move the servo light Lr1 in the focusing direction and the tracking direction which are the thickness direction and the radial direction of the optical disc 10.

In order to move the servo light Lr1 in the focusing direction and the tracking direction, the driving unit 44 may be configured as a two-axis actuator, and the objective lens 100 may be driven in two axes in the focusing direction and the tracking direction. In addition, the drive unit 44 may be configured as a three-axis actuator to drive the objective lens 100 not only for focusing and tracking, but also for radial tilt.

The servo light Lr1 is collected by the objective lens 100 on the reflective film 11 and the reflected servo light Lr2 is received by the first photodetector 79. The reflected servo light received by the first photodetector 79 is reflected. Lr2 reflects the focusing and tracking states.

Although not shown, the first photodetector 79 detects the focus error signal and the tracking error signal, but the main photodetector and the sub-beam include four light receiving regions Ar, Br, Cr, and Dr. to receive the main beam. The first and second sub-photodetectors respectively include two light-receiving regions Er and Fr (Hr and Gr) respectively disposed on both sides of the main photodetector in the radial direction to receive the light.

The focus control may be performed by astigmatism using a signal detected by the main photodetector. The focus error signal FESr using the main beam detection signal received by the main photodetector can be obtained from Equation 1, and the focus error signal FESr is input to a controller (not shown) to provide the objective lens 100. Used to control focus. Hereinafter, for convenience, the light receiving area of the photodetector and the signal detected therefrom are denoted by the same symbol.

FESr = (Ar + Cr)-(Br + Dr)

Tracking control can be achieved by differential push pull method using the signals detected by sub photodetectors 79b and 79c. The tracking error signal DPPr by the differential push-pull method represents an amount by which the servo light Lr1 deviates from the target track, and can be obtained as shown in Equation (2). In Equation 2, k is a gain.

MPPr = (Ar + Dr)-(Br + Cr)

SPPr1 = Er-Fr

SPPr2 = G1-Hr

DPPr = MPPr-k (SPPr1 + SPPr2)

As described above, the servo optical system 70 using the servo light Lr1 irradiates the servo light Lr1 to the reflective film 11 of the holographic information storage medium 10 and uses the detection signal of the reflected servo light Lr2 to provide the objective lens. Control of focus and tracking is performed.

FIG. 6 is a view schematically showing an embodiment of a traveling path of signal light in the recording / reproducing apparatus of FIG. 4, and FIG. 7 is a reference light in the recording mode and the reproducing mode of the recording / reproducing apparatus of FIG. 4. Figure schematically shows an embodiment of the progress path of the.

6 and 7, the second light source 21 of the hologram recording / reproducing optical system emits a second light having a second wavelength, for example, about 405 nm blue light Lb. The blue light Lb is incident on the collimating lens 22 and converted into parallel light. The blue light Lb converted into this parallel light passes through the active half wave plate 26 and is reflected by the polarizing beam splitter 27 or passes through the polarizing beam splitter 27. Here, the case where blue light reflected by the polarization beam splitter 27 is used as the signal light Lb2 and the light transmitted through the polarization beam splitter 27 is used as the reference light Lb1 will be described.

The active half-wave plate 26 is an on / off type half-wave plate, and may be configured to act as a half-wave plate when electricity is applied and not to act as a half-wave plate when electricity is not applied. Therefore, when electricity is applied to function as a half-wave plate, the incident blue light Lb is rotated at a predetermined angle by the active half-wave plate 26, so that the signal light Lb2, which is an S-polarized component, is a polarized beam splitter. Reference light Lb1 reflected by (27) and being a P-polarized component is transmitted through polarization beam splitter 27. Here, in the regeneration mode, no electricity is applied to the active half-wave plate 26, so that the active half-wave plate 26 does not function as a half-wave plate, and thus the blue light Lb emitted from the light source 21 is, for example, All or most of the P-polarized blue light Lb passes through the polarization beam splitter 27 and travels along the path of the reference light Lb1 in the recording mode. Here, it is assumed that the blue light Lb emitted from the second light source 21 is in the P-polarized state.

In another embodiment, the active half-wave plate 26 is formed in a structure in which a rotation driving device is provided on the half-wave plate, and the polarization direction is rotated at a predetermined angle according to the rotation angle to adjust the intensity distribution of the S-polarized light and the P-polarized light. It may be.

 The blue light Lb emitted from the second light source 21 is divided into about 50% of the reference light Lb1 and about 50% of the signal light Lb2 by the polarization beam splitter 27. The split ratio can be adjusted by the active half wave plate 26.

The signal light Lb2 of the S polarized light is reflected by the galvano mirror 51 and converted into p-polarized light by the half-wave plate 52, transmitted through the polarizing beam splitter 53, and the circularly polarized light by the quarter-wave plate 54. Converted and re-reflected by the mirror 55. The re-reflected signal light Lb2 is converted into S-polarized light by the quarter wave plate 54 and reflected by the beam splitter 53 to be incident on the galvano mirror 56.

 The galvano mirrors 51 and 56 are configured to change the angle of the reflected light, and may be configured to adjust the traveling direction of the signal light Lb2 by a controller (not shown).

The signal light Lb2 reflected by the galvano mirror 56 passes through the slit 57 and is incident to the beam expander 58. The beam expander 58 may be composed of two movable lenses 59 and 60. The signal light Lb2 is diverted by the movable lens 59 to be converted into focused light by the movable lens 60, passes through the relay lens 61, enters the half-wave plate 64, and is converted into p-polarized light.

Here, the beam expander 58 serves as a focus shifter for moving the focus of the signal light Lb2 in the thickness direction in the optical information storage layer of the optical disc 10. The beam expander 58 is composed of two movable lenses 59 and 60. The movable lens 59 is configured to move in the optical axis direction by using a stepping motor or a piezo motor and the movable lens 60 is It is configured to move in the optical axis direction by using an actuator similar to the drive unit 44 (the actuator) for the objective lens 100. The movable lens 59 may be configured to perform coarse focus adjustment, and the movable lens 60 may perform initial adjustment relatively fine compared to the movable lens 59. That is, the movable lens 59 moves the focus of the signal light near the target depth in the optical disc 10 and then moves it to the correct position by the movable lens 60. The moving distance of the movable lens 59 may be configured to be larger than the moving distance of the movable lens 60.

 The relay lens 61 is configured to secure the distance between the objective lens 100 and the movable lens 60 of the beam expander 58 and may be formed of two convex lenses 62 and 63.

The P-polarized signal light Lb2 passing through the half wave plate 64 passes through the polarization beam splitter 38 and is incident on the active half wave plate 46. The incident P-polarized signal light Lb2 is rotated at a predetermined angle by an active half-wave plate 46 driven to convert polarized light (for example, electricity is applied), and is converted to mainly include an S-polarized component. The signal light Lb2 of the P polarization may be converted by the active half wave plate 46 to include about 70% of the S polarization component and about 30% of the P polarization component.

The signal light Lb2 is reflected by the mirror 45 and only the S polarization component of the signal light Lb2 is incident on the mirror 42 by the dichroic prism 41 and is, for example, right circularly polarized light by the quarter wave plate 43. Is changed into and is incident on the objective lens 100. The signal light Lb2 is condensed by the objective lens 100 and is reflected by a reflective transmission film (12 of FIG. 1) including a cholesteric liquid crystal layer to form a focal point at Fb.

 With respect to the signal light Lb2, the objective lens 100 can collect the signal light Lb2 and act as a condensing lens having a numerical aperture of about 0.4, for example, by a relationship such as an optical distance from the beam expander 58 or the like.

The signal light Lb2 collected at the focal point Fb diverges and is reincident to the objective lens 100. Here, this reflected signal light is referred to as Lb4. The reflected signal light Lb4 is reflected from the reflective transmission film 12 including the cholesteric liquid crystal layer and has the same right circularly polarized light as the signal light Lb2. The reflected signal light Lb4 is converted into S-polarized light by the quarter wave plate 43, reflected by the mirror 42, the dichroic prism 41, and the mirror 45 and incident on the active half-wave plate 46. The reflected signal light Lb4 of the S-polarized light is converted by the active half wave plate 46 to include, for example, about 30% of the S-polarized component and about 70% of the P-polarized component, and the S-polarized component of the reflected signal light Lb4 Reflected by the polarizing beam splitter 38. The reflected signal light Lb4 of the reflected S-polarized component passes through the relay lens 35 and enters the beam expander 32. The reflected signal light Lb4 is converted into P-polarized light by the half-wave plate 31, is transmitted through the polarization beam splitter 28, is collected by the condenser lens 46, and astigmatism is generated by the cylindrical lens 47. The second photodetector 48 is received.

Since the optical disc 10 has a possibility of deflection and eccentricity, the target track and the corresponding focal position may be changed. As described above, the focus and tracking are controlled by a servo optical system and a controller (not shown) using the servo light which is red light. have. However, the signal light Lb2 may deviate from the position of the focus Fb of the reference light Lb1 by the movement of the objective lens 100. Accordingly, in the signal light optical system 50, the reflected signal light Lb4 according to the focal shift amount of the signal light Lb2 with respect to the focal point Fb of the reference light Lb1 located in the optical information storage layer 13 of FIG. ) To adjust the optical position of various optical components by reflecting the state received by the second photodetector 48.

In the recording mode, for the focus and tracking control of the signal light Lb2, the second photodetector 48 may be provided with four light receiving areas Ab, Bb, Cb, and Db, and the four light receiving areas (4). The reflected signal light Lb4 is detected by Ab, Bb, Cb, and Db. The signal processor (not shown) is configured to perform focus control by the astigmatism method, and the focus error signal FESb, as shown in Equation 3, is detected from the detection signals of the four light receiving regions Ab, Bb, Cb, and Db. Calculate and feed to the controller.

FESb = (Ab + Cb)-(Bb + Db)

The focus error signal FESb expresses the amount of difference in the focus direction between the focus Fb of the reference light Lb1 and the focus of the signal light Lb2.

 Tracking is performed to control by using a push-pull signal, calculates a tracking error signal (RPPb) as in Equation 4, and supplies it to the controller.

RPPb = (Ab + Db)-(Bb + Cb)

This tracking error signal RTPb expresses the amount of difference in the tracking direction between the focus Fb of the reference light Lb1 and the focus of the signal light Lb2.

Meanwhile, as shown in Equation 5, a tangent error signal TTPb necessary for tangential control may also be generated. Tangential control is control for positioning the signal light Lb2 at the focal point Fb of the reference light Lb1 with respect to the tangential direction of the optical disc 10.

TPPb = (Ab + Bb)-(Cb + Db)

 This tangential error signal TTPb expresses the amount of difference in the tangent direction of the optical disc 10 between the focal point Fb of the reference light Lb1 and the focal point of the signal light Lb2.

The controller generates a focus driving signal based on the focus error signal FESb, and supplies the focus driving signal to the movable lens 60 of the beam expander 58, for example, to focus Fb of the reference light Lb1. The movable lens 60 may be focus-controlled to reduce the amount of difference in the focusing direction of the focus of the signal light Lb2 with respect to the focusing direction. In addition, a tracking drive signal is generated based on the tracking error signal RBPb, and the tracking drive signal is supplied to, for example, the galvano mirror 56, so that the signal light Lb2 for the focus Fb of the reference light Lb1 is supplied. The galvano mirror 56 can be tracked to reduce the amount of difference with respect to the tracking direction of the focal point.

In addition, the controller generates a tangential drive signal based on the tangential error signal TTPb, and supplies the tangential drive signal to the galvano mirror 51, so that the signal light with respect to the focal point Fb of the reference light Lb1 is generated. The galvano mirror 51 can be tangentially controlled to reduce the amount of difference with respect to the tangential direction of the focus of Lb2).

Accordingly, the signal light optical system 50 is configured to irradiate the holographic information storage medium 10 with the signal light Lb2 and receives the reflected signal light Lb4 reflected by the reflective transmission film 12 of FIG. 1. The light receiving result is supplied to the signal processing unit, and the control unit controls the focus of the beam expander 58 and the relay lens 61 and the galvano mirror to form the focus of the signal light Lb2 at the focus Fb of the reference light Lb1. Tangential and tracking controls of 51 and 56 are possible.

Meanwhile, referring to FIG. 7, in the reference light optical system 20, the blue light Lb emitted from the light source 21 becomes parallel light through the collimating lens 22 and passes through the active half wave plate 26. It includes an S polarization component and a P polarization component. The S-polarized component of the blue light Lb is reflected by the polarization beam splitter 27 and used as the signal light Lb2 as described above.

The P-polarized component of the blue light Lb may pass through the polarization beam splitter 27 and be used as the reference light Lb1. The reference light Lb1 transmitted through the polarization beam splitter 27 is incident on the polarization beam splitter 28. The reference light Lb1 of the P-polarized light transmitted through the polarization beam splitter 28 is converted into the left circularly polarized light by the quarter wave plate 29, reflected by the mirror 30, and again by the quarter wave plate 29. It is converted into S-polarized light and reflected by the polarization beam splitter 28 to travel toward the half-wave plate 31. The reference light Lb1 of the S-polarized light is converted into P-polarized light by the half-wave plate 31 and is incident on the beam expander 32.

Here, the mirror 30 is provided to be movable, and the optical path length of the reference light Lb1 and the signal light Lb2 can be adjusted by changing the length of the optical path of the reference light Lb1 by the movement of the mirror 30. have. In order to match the optical path lengths of the reference light Lb1 and the signal light Lb2, the mirror 55 in the signal light optical system 50 is driven, or in the mirror 55 and the reference light optical system 20 in the signal light optical system 50. Both mirrors 30 may be driven. In the case of using a laser diode as the light source 21, since the interference distance of the laser diode is about several hundred microns, when the difference in the optical path length between the reference light Lb1 and the signal light Lb2 is greater than or equal to the interference light, the reference light Lb1 and The recording mark (hologram) formed at the focus of the signal light Lb2 may not be recorded well. Therefore, in order to form a good hologram, for example, it is necessary to adjust the mirror 30 so that the difference between the optical path lengths of the reference light Lb1 and the signal light Lb2 is equal to or less than the interference distance.

The reference light Lb1 of the P-polarized light incident on the beam expander 32 is emitted by the movable lens 33 and rehydrated by the movable lens 34. The reference light Lb1 via the beam expander 32 passes through the relay lens 35 and is incident on the polarizing beam splitter 36. Since the reference light Lb1 has P polarization as described above, the polarizing beam splitter It penetrates 36 and enters the shutter 39. Here, the beam expander 32 and the relay lens 35 function substantially the same as the beam expander 58 and the relay lens 61 in the signal light optical system 50. In addition, the beam expander 32 forms a focus shifting unit for moving the reference light Lb1 along the thickness direction of the optical information storage layer of the optical disc 10. The beam expander 32 is composed of two movable lenses 33 and 34 moving in the optical axis direction. The movable lens 33 performs coarse focus adjustment and the movable lens 34 finely focuses. Perform the adjustment.

The shutter 39 is configured to block or pass the reference light Lb1 by the controller. When the reference light Lb1 passes through the shutter 39, the reference light Lb1 is reflected by the dichroic prism 40 as blue light of P polarization, is transmitted through the dichroic prism 41 and is incident on the mirror 42. The reference light Lb1 is reflected by the mirror 42, converted into left circularly polarized light by the quarter wave plate 43, and collected by the objective lens 100 on the optical disk 10.

 The objective lens 100 may serve as a condenser lens having a numerical aperture of about 0.65, for example, by concentrating the reference light Lb1 and an optical distance with the beam expander 32. Here, the numerical aperture of the objective lens 100 with respect to the reference light Lb1 is larger than the numerical aperture with respect to the signal light Lb2, because the reference light Lb1 is collected by the objective lens 100 and is immediately focused on the focal point Fb. On the other hand, the signal light Lb2 is focused by the objective lens 100 and reflected by the reflective transmission film 12 of FIG. 1 and then focused on the focal point Fb, so that the signal light Lb2 is focused. This is because the focal length of? Must be larger than the focal length of the reference light Lb1. However, the reference light Lb1 is directly focused on the focus Fb, and the signal light Lb2 is reflected by the reflective transmission film 12 and then focused on the focus Fb by way of example. Examples are not limited to this.

 During recording, little of the reference light Lb1 is reflected by the reflective transmission film 12 of the optical disk 10 and returned to the objective lens 100. The reflective transparent film (12 of FIG. 1) including the cholesteric liquid crystal layer mainly has a property of reflecting only right circularly polarized light, so that reference light Lb1 incident on the optical disk 10 with left circularly polarized light is hardly reflected.

In the regeneration mode, the active half wave plate 26 is turned off so as not to function as a half wave plate, and the blue light Lb emitted from the second light source 21 passes through the active half wave plate 26 without changing polarization. It passes through the polarization beam splitter 27 and progresses along the optical path of the reference light Lb1 in the recording mode. Therefore, since the blue light used in the reproduction mode is the same as the reference light Lb1 in the recording mode, it is assumed that the blue light in the reproduction mode is the reference light Lb1.

The mark recorded in the optical information storage layer of the optical disc 10, that is, the reference light (hereinafter referred to as the reproduction light) for reproducing the hologram, is incident on the objective lens 100 during hologram reproduction. The reference light Lb1 is incident on the optical disc 10 in a left circularly polarized state, and the regenerated light reflected by the hologram changes only the traveling direction of the light, and does not change the rotation direction of the electric field vector, resulting in light of right circularly polarized light. The regenerated light of the right circularly polarized light is converted into S-polarized light by the quarter wave plate 43 and then reflected by the mirror 42, reflected by the dichroic prism 41, and reflected by the mirror 45, thereby forming an active half-wave ( 46). At the time of reproduction, since the active half wave plate 46 does not apply electricity and thus does not function as a half wave plate, the regenerated light of S polarized light passes through the active half wave plate 46 without changing polarization and is reflected by the polarization beam splitter 38. And enters the relay lens 35. The regenerated light of the S-polarized light passing through the relay lens 35 is converted into a parallel beam while passing through the beam expander 32, is converted into P-polarized light by the half-wave plate 31, and then transmitted through the polarizing beam splitter 28. . The regenerated light of the transmitted P-polarized light is collected by the condenser lens 46 and passed through the cylindrical lens 47 and received by the second photodetector 48. The recording mark hologram information recorded in the predetermined recording layer can be known from the reproduction light signal detected by the second photodetector 48.

The recording of information in the information recording / reproducing apparatus according to the embodiment of the present invention as described above is performed as follows.

The servo optical system 50 irradiates the servo disk Lr1 to the optical disk 10 and performs focusing and tracking control of the objective lens 100 based on the detection result of the reflected servo light Lr2 reflected by the reflecting film 11. The focus Fr of the servo light Lr1 is followed by the target track.

In addition, the signal light optical system 50 irradiates the blue signal light Lb2 to the optical disc 10, and the focus Fb of the signal light Lb2 is positioned on the target track by the objective lens 100 which is position-controlled. By adjusting the position of the movable lens 59 of the beam expander 58 to adjust the target depth corresponding to the focus Fb, the blue signal light Lb2 is positioned at the focus Fb.

In the reference light optical system 20, the reference light Lb1 is irradiated onto the optical disk 10, and when the reference light Lb1 passes through the reference light Lb1 by adjusting the position of the movable lens 33 of the beam expander 32 and controlling the shutter 39. The reference light Lb1 is positioned at the focal point Fb.

Here, the recording power control of the second light source 21 detects and adjusts the light received by the front photodetector 25. A part of the light emitted from the second light source 21 is branched by the beam splitter 23, focused by the focusing lens 24, and received by the front photodetector 25.

 There is a possibility that the signal light Lb2 may deviate from the desired focus Fb position due to the eccentricity and deflection of the optical disc 10. In consideration of this, tangential and tracking control and focus control are performed by the galvano mirrors 51 and 56 and the movable lens 60 of the beam expander 58 based on the detection result of the reflected signal light Lb4.

By the above process, in the state where the reference light Lb1 and the signal light Lb2 are merged at the focal point Fb, the mirror 30 is moved to add an optical path length difference between the reference light Lb1 and the signal light Lb2. Adjust below the interference distance. Then, a good recording mark hologram is recorded.

Further, when the target depth is adjusted to record information in the plurality of recording layers, that is, by the same process as described in FIG. That is, when the recording layer is changed from the first focus position Fb to the second focus position Fb ', the focus shifter of the signal light optical system 50 and the focus shifter of the reference light optical system 20 operate together, and the signal light The focus of Lb2 and the focus of the reference light Lb1 are shifted. After the focus of the reference light Lb1 and the signal light Lb2 is matched at the second focal point Fb ', the mirror 30 is similarly moved to interfere with the optical path length difference between the reference light Lb1 and the signal light Lb2. By adjusting below the distance, a good recording mark hologram is recorded.

The reproduction of information in the information recording / reproducing apparatus according to the embodiment of the present invention as described above is performed as follows.

The servo optical system 50 irradiates the servo light Lr1 to the optical disc 10 and performs focusing and tracking control of the objective lens 100 based on the detection result of the reflected servo light Lr2 reflected by the reflecting film 11. The focal point Fr of the servo light Lr1 follows the target track.

The reference light Lb1 is irradiated to the optical disc 10 by the reference light optical system 20. The focal point Fb of the reference light Lb1 may be collected by the objective lens 100 that is position-controlled and positioned on the target track. Further, coarse control is performed by the movable lens 33 of the beam expander 32, and fine control is performed by the movable lens 34, so that the focus Fb position of the reference light Lb1 is adjusted. Adjusted.

At the time of regeneration, since no electricity is applied to the active half-wave plate 26 and thus does not function as a half-wave plate, the blue light Lb emitted from the second light source 21 becomes all or most of the reference light Lb1, thereby increasing the reproduction efficiency. The reference light Lb1 is passed through the control of the shutter 39.

The reference light Lb1 is irradiated to the recording mark hologram, and the reproduction light is generated by the recording mark hologram, and the reproduction light is detected by the second photodetector 48 to obtain a reproduction signal. In this case, if the active half-wave plate 46 is not supplied with electricity to prevent the active half-wave plate 46 from functioning as the half-wave plate, the reproduction light receiving efficiency can be increased.

The present invention has been described with reference to the embodiments shown in the drawings for ease of understanding, but this is merely exemplary, those skilled in the art that various modifications and equivalent other embodiments are possible from this. I will understand. Therefore, the true technical protection scope of the present invention will be defined by the appended claims.

1 is a view showing a schematic structure of a hologram optical disc that can be applied to a recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a view schematically showing a recording mark hologram formed in an optical information storage layer of the optical disk of FIG. 1 by interference of reference light and signal light.

3 is a diagram schematically illustrating a process of recording information in a plurality of recording layers in the recording / reproducing method according to the embodiment of the present invention.

4 is a diagram schematically showing the configuration of a recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 5 schematically illustrates an embodiment of a traveling path of servo light in the servo optical system in the recording / reproducing apparatus of FIG. 3.

FIG. 6 is a view schematically showing an embodiment of a propagation path of signal light in a recording mode in the recording / reproducing apparatus of FIG. 3.

FIG. 7 is a view schematically showing an embodiment of a traveling path of reference light in the recording / reproducing mode of the recording / reproducing apparatus of FIG. 3.

Claims (15)

A recording / reproducing apparatus for an optical disc having an optical information storage layer, A reference light optical system for focusing a reference light in the optical information storage layer, the reference light optical system including an objective lens facing the optical disc; A signal light optical system for forming a focus of a signal light in the optical information storage layer, the signal light optical system including the objective lens; And a servo optical system for irradiating servo light onto the optical disk and receiving reflected light to perform focusing and tracking control of the objective lens. The reference light optical system includes a first focusing unit for moving a focus of the reference light, The signal light optical system includes a second focusing unit for moving the focus of the signal light; The first focusing position where the focus of the reference light and the focus of the signal light coincide is formed in the optical information storage layer by moving in the thickness direction of the optical information storage layer to record the information, thereby recording the information in the plurality of recording layers, When the first focusing position is moved to a second focusing position having a different thickness direction position of the optical information storage layer, the first and second focusing are performed such that the focus of the reference light and the focus of the signal light move simultaneously to the second focusing position. Recording / playback device with eastern drive. The method of claim 1, And a reflection film for physically distinguishing the plurality of recording layers is not formed on the optical disc. The method of claim 2, And an optical information storage layer of the optical disc, wherein the optical information storage layer is made of a photosensitive material capable of hologram recording. delete The method of claim 1, And the first and second focus moving parts are driven such that, when the first focus position is moved, a focus error signal due to a mismatch between the focus of the first light and the focus of the second light is within a negative feedback linear section. The method of claim 5, And the servo operation of the servo optical system is maintained when the first focusing position is moved. The method according to any one of claims 1 to 3, 5 and 6, In order to prevent a change in a direction other than a focusing direction which is a thickness direction of the optical information storage layer when the first focusing position is moved, a galvano mirror capable of adjusting a tracking direction and a tangential direction perpendicular to the focusing direction is further added. And a recording / reproducing apparatus. The method according to any one of claims 1 to 3, 5 and 6, And the first focusing unit comprises two movable lenses movable along the optical axis direction. The method of claim 8, Wherein one of the two movable lenses performs coarse focus adjustment and one performs fine focus adjustment. The method according to any one of claims 1 to 3, 5 and 6, And the second focusing unit comprises two movable lenses movable along the optical axis direction. The method of claim 10, Wherein one of the two movable lenses performs coarse focus adjustment and one performs fine focus adjustment. A recording / reproducing method for an optical disc having an optical information storage layer, Forming a focus of a reference light and a focus of a signal light on the optical information storage layer; Moving the focus of the reference light and the focus of the signal light so as to coincide with each other at the first focusing position, and changing the first focusing position along the thickness direction of the optical information storing layer in the optical information storing layer; Include, When the first focusing position is changed to a second focusing position having a different thickness direction position of the optical information storage layer, the focus of the first light and the focus of the second light are simultaneously moved to the second focusing position and the information is transmitted to a plurality of recording layers. Recording / playback method for recording. delete The method of claim 12, And a focus error signal caused by a mismatch between the focus of the first light and the focus of the second light when the first focus position is shifted so that the focus of the first light and the focus of the second light are shifted so that the focus error signal is within the negative feedback linear section. The method of claim 14, And a servo drive operation for the optical disk of the objective lens forming the focal point of the reference light and the focal point of the signal light when the first focusing position is moved.

Images